260 A Manual of Veterinary Physiology. 



on the cerebro-spinal nerves they are to be found, though 

 in all cases limited to the sensory branch only. The struc- 

 ture of the ganglia of a sympathetic and cerebro-spinal 

 nerve is not identical : in the former the nerves composing 

 it are both medullated and non-medullated, and the nerve 

 cells of the ganglia are multipolar ; in the cerebro-spinal 

 ganglia the nerve cells are only unipolar, and the nerve 

 libres medullated on entering, but non-medullated on leav- 

 ing it. The one pole or process issuing from the nerve cell 

 after a time divides forming a T-piece, one end of the T 

 probably running to the nerve centre, and one to the 

 periphery. The cells are really lateral appendages to the 

 fibres, and we again repeat they are found on sensory and 

 not on motor nerves. The only known function of ganglia, 

 whether cerebro-spinal or sympathetic, is for the purpose of 

 nerve nutrition ; no impulses originate in ganglia, nor can 

 they serve as centres for reflex action; in other words they 

 are not nerve centres. 



Nerve Terminations. — We have alluded to the terminal end 

 organs of nerves, and attributed to these the special function 

 of the nerve ; we must therefore briefly refer to them. A well- 

 known form of nerve termination is the Pacinian corpuscle ; 

 it is found both in connection with cerebro-spinal and 

 sympathetic nerves. Touch corpuscles are found in the 

 muzzle of the horse and other animals, and probably also 

 in the sensitive structures of the foot ; end bulbs are found 

 in the generative organs ; bodies like Pacinian exist in 

 tendons ; besides these, there are motor terminations, such 

 as the motorial end plates in muscle, and secretory fibre 

 terminations in the various glands ; lastly, there are endings 

 in the nerves of special sense, such as the rods and cones of 

 the retina, etc. 



Spinal Cord. 

 The spinal cord extends from the alius to about the 

 second or third sacral vertebra. It is completely enclosed 



by a dense membrane, the dura mater. The canal in which 

 it is lodged is very much larger than the cord, especially at 



